1. Field of the Invention
The present invention relates generally to a galling-resistant threaded connection formed of male- and female-type threaded connectors and a process for making the male- and female-type threaded connectors, and more specifically relates to a galling-resistant threaded joint for tubular components for use in connecting tubular components and particularly tubular components used for drilling and operating hydrocarbon wells.
2. Description of the Related Art
A tubular component which is “used for drilling and operating hydrocarbon wells” means any element that is substantially tubular in form intended to be connected to another element of the same type or otherwise to finally constitute either a string for drilling a hydrocarbon well or a riser intended for maintenance, such as work-over risers, or for operation, such as production risers, or for a casing string or tubing string used in the operation of wells. The invention is also applicable to components used in a drill string, such as drill pipes, heavy weight drill pipes, drill collars and the portions of pipe connections and heavy weight pipes known as tool joints.
A tool joint is a heavy coupling element for pipe, typically drill pipe, made of special alloy steel. Tool joints have coarse, tapered threads and seating shoulders designed to sustain the weight of the drill stem, withstand the strain of frequent coupling and uncoupling, and provide a leakproof seal. The male section of the joint, or the pin, is attached to one end of a length of drill pipe, and the female section, or box, is attached to the other end. The tool joint may be welded to the end of the pipe or screwed on or both. Joints of pipe are coupled together by means of tool joints.
The pin tool joint has a male (external) thread formed thereon, and the box tool joint has a female (internal) thread formed therein. A coupling or connection is formed by threadably engaging the pin tool joint of one tubular component with the box tool joint of a second tubular component. To make-up the connection, one tubular component is rotated relative to the other tubular component. To breakout the connection, the direction of relative rotation is reversed.
Today, several deep oil wells in offshore oil fields have reached depths of 20,000′-30,000′ (feet). Many of the pipes and casings employed in the well are threaded tubulars having a length of approximately 30′. For example, a joint of drill pipe used to facilitate the drilling of the wellbore typically has a length of approximately thirty feet (30′) or forty-five feet (45′). Thus, it is easy to see that the total string of drill pipe may comprise hundreds and possibly more than a thousand joints of pipe threaded together in some deep wells.
The oil field tubular threaded joints are subjected to tensile forces in the axial direction caused by the weight of the connected joint string and the individual joints themselves. Additionally, the threaded joints are subjected to internal and external pressures and excessive temperatures. Typically, deeper wells have higher temperatures and higher pressures than more shallow wells. The threaded connections of pipe located within the borehole exposed to these higher temperatures and/or higher pressures must withstand such severe conditions while maintaining gas tightness.
During the process of lowering tubing or casing into a well, it is sometimes necessary to breakout a pipe joint which has been made up to another tubular member, to lift the pipes out of the well, and subsequently to again make-up the connection, and then re-lower the pipe into the well. During drilling of the well, the threaded tubular components making up the drill string may have to undergo several make-up and breakout cycles. Make-up operations are generally carried out under high axial load. For example, the weight of a pipe joint thirty (30) or forty-five (45) feet long to be connected by the threaded connection may be localized by a slight misalignment of the axis of the threaded elements to be connected. This may induce a risk of galling at the threaded zones.
Traditionally, the threaded zones are protected against galling during make-up and breakout operations in the field. Initially, the threaded zones are stripped of any grease which may have been previously applied to protect against corrosion. The connection contact surfaces are cleaned and free of drilling fluids and any other contaminant residues because the solids that are present in the drilling fluids and muds can promote galling and degrade the galling resistance properties of the compound grease that is applied next. Compound grease is applied on-site to the contact surfaces of the threaded joint. The compound grease is a viscous liquid lubricant containing large amounts of powders of heavy metals such as zinc, lead, and copper. Compound grease is commonly referred to as “pipe dope.” The pipe dope is applied liberally and uniformly to the entire contact surface of both the pin and box and worked into the thread roots and completely covers the shoulder surfaces. The compound grease, specified by American Petroleum Institute standards API Bulletin 5A2 or 5A3, is required to be able to impart rust prevention to the contact surface to which the compound grease was applied and also improves the thread seal and provides lubrication during the make-up of the connection.
However, when make-up of a threaded joint for pipes is carried out, compound grease which has been applied is washed off or overflows to the exterior surface, and there is the possibility of it producing harmful effects on the environment and especially on sea life, particularly due to the harmful heavy metals. Also, the process of applying compound grease worsens the working environment, and there is a concern of it having harmful effects on humans.
Thus, the step of applying the pipe dope on-site to the threaded portions takes time—time which is valuable and costly—and manpower. Additionally, the use of such compound greases, loaded with heavy and/or toxic metals such as lead, suffers from the disadvantage of causing pollution of the wells and of the environment, since excess grease is ejected from the threaded connection during make-up.
In the past, it has been proposed to carry out various types of surface treatment such as nitriding, various types of plating including zinc plating and composite plating, and phosphate chemical conversion treatment on the contact surface of a threaded joint for pipes to form one or more layers in order to increase the retention of compound grease and improve sliding properties. However, as described above, the use of compound grease poses the threat of harmful effects on the environment and humans.
It is understood in the prior art that a break-in procedure should be used for new connections in the field. Typically, this procedure comprises 2 to 3 make-ups of the connection prior to running the pipe joint. The 2 to 3 make-ups may be slow speed make-ups at 50-75% of the final running make-up torque. This practice is thought to burnish and work harden the connection surfaces prior to applying full contact stress to improve resistance to galling. However, this practice has not been found to provide lasting galling resistance.
It is desirable to have a tubular threaded joint connection that is resistant to galling and remains resistant to galling after numerous connection make-ups and breakouts. It is desirable to have a galling resistant threaded connection that does not use compound grease or other chemicals, is environmentally friendly, and saves time and manpower during the connection make-up operation. It is desirable to have a galling resistant threaded connection that can withstand high temperature exposure.